Integrated circuit coolant microchannel assembly with manifold member that facilitates coolant line attachment

ABSTRACT

An apparatus includes a microchannel structure having microchannels formed therein. The microchannels are to transport a coolant and to be proximate to an integrated circuit to transfer heat from the integrated circuit to the coolant. The apparatus also includes a plurality of walls coupled to the microchannel structure to define a manifold. The manifold is in communication with at least a plurality of the microchannels. The plurality of walls includes a side wall. The side wall has a port therein. The port allows the coolant to flow in a direction that is either into the manifold or out of the manifold.

BACKGROUND

As microprocessors advance in complexity and operating rate, the heatgenerated in microprocessors during operation increases and the demandson cooling systems for microprocessors also escalate. It has beenproposed to cool microprocessors with cooling systems that circulate aliquid coolant through a microchannel cold plate that is thermallycoupled to the microprocessor die. One issue that may be encountered inmicrochannel cooling systems is potential difficulty in connecting tubesfor the coolant path to the potentially delicate cover of a microchannelassembly. Techniques have been proposed for attaching fittings forcoolant tubes to the microchannel assembly cover, but this technique maynot be suitable for application to high volume manufacturing ofmicrochannel cooling systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially exploded schematic vertical cross-sectional viewof a microchannel assembly according to some embodiments.

FIG. 2 is a schematic horizontal cross-sectional view of themicrochannel assembly, taken at line II-II in FIG. 1.

FIG. 3 is a view similar to FIG. 1 of a microchannel assembly accordingto some other embodiments.

FIG. 4 is a schematic horizontal cross-sectional view of themicrochannel assembly of FIG. 3, taken at line IV-IV in FIG. 3.

FIG. 5 is a schematic horizontal cross-sectional view of a microchannelassembly according to still other embodiments.

FIG. 6 is a schematic vertical cross-sectional view of the microchannelassembly of FIG. 5, taken at line VI-VI in FIG. 5.

FIG. 7 is a block diagram showing a die with additional components of acooling system according to some embodiments.

FIG. 8 is a block diagram of a computer system according to someembodiments that includes an example of an integrated circuit dieassociated with a cooling system as in one or more of FIGS. 1-7.

DETAILED DESCRIPTION

FIG. 1 is a partially exploded schematic vertical cross-sectional viewshowing a microchannel assembly 100 according to some embodiments,thermally coupled via a thermal interface material (TIM) 105 to anIntegrated Circuit (IC) 110. FIG. 2 is a schematic horizontalcross-sectional view of the microchannel assembly 100, taken at lineII-II in FIG. 1. The IC 110 may be associated with, for example, anINTEL® PENTIUM IV processor.

The microchannel assembly 100 includes a microchannel structure 112having microchannels 114 (FIG. 2) formed therein. The microchannels 114are channels or passages each having a width of about 20 to 500micrometers, although other widths may be used. The microchannels 114transport (e.g., allow to flow therein) a coolant (not shown). Themicrochannel structure 112 may be any body, such as a metal or siliconcold plate in which microchannels are formed and which is to be mountedon the back-side of a microchip such as the IC 110 so that themicrochannels are proximate to the IC to transfer heat from the IC tothe coolant. The IC 110 may be thinned to reduce thermal resistancebetween the transistors and the microchannels. The microchannelstructure 112 may alternatively be the microchip die itself havingmicrochannels formed in a rear surface thereof.

In some embodiments, the microchannels 114 may have a height of about300 microns and a width of about 100 microns, but other dimensions ofthe microchannels 114 are possible. In a practical embodiment, thenumber of microchannels may be much more than the relatively fewmicrochannels depicted in the drawing. The microchannels may, but neednot, all be straight and parallel to each other. In general, FIGS. 1 and2 and the other drawings herein are not to scale.

The microchannel assembly 100 also includes a lid or cover 120 (FIG. 1)that effectively closes the top of the microchannels 114 formed in themicrochannel structure 112.

The microchannel assembly 100 further includes an inlet manifold member125 and an outlet manifold member 130. The inlet manifold member 125 iscoupled to a front end 135 of the microchannel structure 112 and also tothe corresponding end of the lid 120. The coupling of the inlet manifoldmember 125 to the microchannel structure and lid may be done by aliquid-tight sealing arrangement 140, such as an O-ring, solder or anepoxy adhesive.

The inlet manifold member 125 includes a plurality of walls to define aninlet manifold 141 at the front end 135 of the microchannel structure112. The inlet manifold is in communication with all of themicrochannels 114. The plurality of walls that constitute the inletmanifold member 125 includes a main side wall indicated at 142, 144 inFIG. 1 and at 146, 148 in FIG. 2. The plurality of walls also includes aleft side wall 150 and a right side wall 152. It will be understood thatall of the main side wall, the left side wall and the right side wallare to be considered “vertical walls”, where the vertical direction (asseen in FIG. 1) is the direction from the microchannel structure 112 tothe IC 110.

The main side wall has an inlet port 154 formed therein (e.g., at acentral location in the main side wall) to allow coolant (not shown) toflow into the inlet manifold 141. The inlet port 154 may be integrallyformed in the main side wall, or may be formed by molding the main sidewall around a suitable fitting, which is not separately shown. The inletport 154 may be configured to facilitate connection of a coolant line(not shown in FIGS. 1 and 2) which transports coolant from a pump (notshown) to the microchannel assembly 100.

The inlet manifold member 125 also includes a top wall 156 (FIG. 1) anda bottom wall 158, which are horizontal walls.

In some embodiments, the inlet manifold member may be formed as a singleunitary body, formed for example of a metal such as copper, or siliconor molded plastic.

The outlet manifold member 130 is shown separately from the microchannelstructure 122 in FIG. 1 for purposes of illustration, but in practicemay be coupled to the rear end 160 of the microchannel structure 122, asshown in FIG. 2. The outlet manifold member is also coupled to the lid120. The same sort of sealing arrangement (indicated at 162) may beemployed for the outlet manifold member as was described above inconnection with the inlet manifold member. In some embodiments, theoutlet manifold member may be a mirror image of the inlet manifoldmember, or even identical in form to the inlet manifold member.

The outlet manifold member 130 includes a plurality of walls to definean outlet manifold 164 at the rear end 160 of the microchannel structure112. The outlet manifold is in communication with all of themicrochannels 114. The plurality of walls that constitute the outletmanifold member 130 includes a main side wall indicated at 166, 168 inFIG. 1 and at 170, 172 in FIG. 2. The plurality of walls that constitutethe outlet manifold member 130 also includes a left side wall 174 and aright side wall 176. The main side wall and right and left side walls ofthe outlet manifold member 130 are all vertical walls.

The main side wall of the outlet manifold member 130 has an outlet port178 formed therein (e.g., at a central location in the main side wall)to allow coolant to flow out of the outlet manifold 164. The outlet port178 may be configured to facilitate connection of a coolant line (notshown in FIGS. 1 and 2) which transports coolant from the microchannelassembly 100 to the pump that was mentioned above.

The outlet manifold member 130 also includes a top wall 177 and a bottomwall 179, which are horizontal walls.

As was indicated with respect to the inlet manifold member, the outletmanifold member may be formed as a single unitary body. The outletmanifold member may, but need not, be formed of the same material as theinlet manifold member.

In operation, a pump (which is not shown) may pump a liquid coolant (notshown) through an inflow coolant line (not shown) that is coupled to theinlet port 154. The coolant may flow through the inlet port in thedirection indicated by arrows 180 (FIG. 1) and 182 (FIG. 2) into theinlet manifold 125. It will be recognized that the direction indicatedby arrows 180, 182 is a horizontal direction that is parallel to thelength dimension of the microchannels 114. The coolant is distributed bythe inlet manifold 125 among the microchannels 114 and flows out of theinlet manifold 125 into the microchannels 114 in the same directionindicated by the arrows 180, 182. The coolant flows through themicrochannels 114 in the same direction indicated by the arrows 180,182. While the coolant flows through the microchannels 114, heatgenerated by transistors (not separately shown) on the front side of theIC 110 is transferred through the TIM 105 and the microchannel structure112 to the coolant, thereby heating the coolant. The heated coolant,still flowing in the direction indicated by the arrows 180, 182, flowsout of the microchannels 114 and into the outlet manifold 130. Further,the coolant flows in the direction indicated by arrows 180, 182 out ofthe outlet manifold 130 via the outlet port 178, as further indicated byarrows 184 (FIG. 1) and 186 (FIG. 2). The coolant flows from the outletport 178 to a heat exchanger (not shown) via an outflow coolant line(not shown) that is coupled to the outlet port 178. A fan (not shown)directs air flow through the heat exchanger to remove heat from thecoolant, thereby cooling the coolant, which is then pumped back to themicrochannel assembly 100.

To efficiently facilitate a transfer of heat, a coolant with arelatively high thermal conductivity and high heat capacity may be used.Moreover, it may be beneficial if the coolant is relatively inexpensiveand easy to pump. Note that water has a relatively high thermalconductivity, a relatively high heat capacity, is relativelyinexpensive, and can be readily pumped.

The manifold members 125, 130 may facilitate high volume manufacturingof the microchannel assembly 100 and the cooling system of which it is apart by conveniently providing ports to which the coolant circulationlines may be coupled.

In other embodiments, illustrated in FIGS. 3 and 4, a modifiedmicrochannel assembly 100′ has only one manifold member 302, coupled toa front end 304 of the microchannel structure 112′, rather than the twomanifold members coupled to opposite ends of the microchannel structure112 as in the embodiments of FIGS. 1 and 2. In the microchannelstructure 112′ shown in FIGS. 3 and 4, the rear end 306 of themicrochannel structure 112′ is closed by a rear wall 308 of themicrochannel structure 112′. The intake ends 310 of the microchannels114 (as seen in FIG. 4) are spaced from the rear wall 308 so that anintake manifold 312 is formed between the rear wall 308 and the intakeends 310 of the microchannels 114. The intake manifold 312 is incommunication with the microchannels 114.

The microchannel assembly 100′ includes a lower lid 314 (FIG. 3) whichis coupled to the microchannel structure 112′ to close the tops of themicrochannels 114. The microchannel assembly 100′ also includes an upperlid 316 which is spaced above the lower lid 314 to form a coolantpassage 318 between the lids 314, 316. The upper lid 316 is coupled tothe rear wall 308 and the side walls 320, 322 (FIG. 4) of themicrochannel structure 112′ to close the top of the microchannelassembly 100′.

The manifold member 302 includes a plurality of walls to define anoutlet manifold 324 at the front end 304 of the microchannel structure112′. The outlet manifold 324 is in communication with all of themicrochannels 114 of the microchannel structure 112′. The plurality ofwalls that constitute the manifold member 302 includes a main side wallindicated at 326, 328 in FIG. 3 and at 330, 332 in FIG. 4. The pluralityof walls also includes a left side wall 334 and a right side wall 336.The main side wall and the left and right side walls are vertical walls.

The main side wall of the manifold member 302 has an inlet port 338formed therein (e.g. at an upper central location in the main side wall)to allow coolant to flow into the passage 318 and via the passage 318 tothe intake manifold 312 at the rear end 306 of the microchannelstructure 112′. (It will be noted that the rear end 306 of themicrochannel structure 112′ is opposite to the front end 304 of themicrochannel structure 112′.) The main side wall of the manifold 302also has an outlet port 340 formed therein (e.g., at a central locationin the main side wall) to allow coolant to flow out of the outletmanifold 324. Each of the inlet port 338 and the outlet port 340 may beintegrally formed in the main side wall, or may be formed by molding themain side wall around a suitable fitting, which is not separately shown.The inlet port 338 may be configured to facilitate connection of acoolant line (not shown in FIG. 3) which transports coolant from a pump(not shown) to the microchannel assembly 100′. The outlet port 340 maybe configured to facilitate connection of a coolant line (not shown inFIGS. 3 and 4) which transports coolant from the microchannel assembly100′ to the heat exchanger.

The manifold member 302 also includes a top wall 342 (FIG. 3) and abottom wall 344, which are both horizontal walls, as well as ahorizontal dividing wall 345 to isolate the inlet port 338 from theoutlet port 340.

The manifold member 302 may be coupled to the microchannel structure112′ via liquid-tight sealing arrangements as indicated at 346 and 348.As in the previous embodiment, the sealing arrangement at 346 may be anO-ring, solder or an epoxy adhesive, for example. The sealingarrangement at 348 may, for example, be formed of solder or an epoxyadhesive.

In some embodiments, the manifold member 302 may be formed as a singleunitary body, formed for example of a metal such as copper, or siliconor molded plastic.

The operation of a cooling system that includes the microchannelassembly 100′ may be generally the same as the operation described abovein regard to the microchannel assembly 100, except that the flow ofcoolant into, through and out of the microchannel assembly 100′ issomewhat different. Referring to FIG. 3, the coolant flows through theinlet port 338 from the inflow coolant line (not shown) that is coupledto the inlet port 338. The flow of the coolant into the inlet port is inthe horizontal direction indicated by arrow 350. The coolant continuesto flow in the same direction from the front end 304 of the microchannelstructure 112′ to the rear end 306 of the microchannel structure 112′via the passage 318 which is above the microchannels 114 (FIG. 4).Continuing to refer to FIG. 3, the coolant flows from the passage 318into the intake manifold 312 and from the intake manifold 312 into theintake ends 310 (FIG. 4) of the microchannels 114. The coolant flowsthrough the microchannels 114 in a horizontal direction that is oppositeto the direction indicated by arrow 350 (FIG. 3). The coolant flows outof the microchannels 114 and into the outlet manifold 324. From theoutlet manifold 324, the coolant flows out of the outlet port 340, inthe direction indicated by arrow 352, which is the same direction inwhich the coolant flowed from the intake manifold 312 into themicrochannels 114, as well as through the microchannels 114 and into theoutlet manifold 324. The coolant is transported away from the outletport 340 via an outflow coolant line (not shown) that is coupled to theoutlet port 340.

In other embodiments, illustrated in FIGS. 5 and 6, a microchannelassembly 100″ may have only a single manifold member 402, as in theembodiments of FIGS. 3 and 4, but the inlet port 404 and the outlet port406, formed in the main side wall 408 of the manifold member 402, may behorizontally spaced from each other, as seen in the horizontalcross-sectional view of FIG. 5, rather than being spaced vertically fromeach other, as in the embodiment of FIGS. 3 and 4 (see the verticalcross-sectional view of FIG. 3).

Referring to FIG. 5, the manifold member 402 may include a plurality ofwalls, including main side wall 408, to define both an inlet manifold410 and an outlet manifold 412, both manifolds 410, 412 being at thefront end 414 of the microchannel structure 112″. The inlet manifold isin communication with a first subset 416 (FIG. 5) of the microchannels114 formed in the microchannel structure 112″. The outlet manifold 412is in communication with a second subset 418 of the microchannels 114formed in the microchannel structure 112″, with the second subset beingall of the microchannels that are not in the first subset 416.

The microchannel structure 112″ is closed at its rear end 420 by therear wall 422 of the microchannel structure 112″. The rear wall 422 isspaced from the microchannels 114 to form an intermediate manifold 423at the rear end 420 of the microchannel structure 112″. The intermediatemanifold 423 is in communication with all of the microchannels 114. (Asbefore, it will be noted that the rear end 420 is opposite to the frontend 414 of the microchannel structure 112″.)

The plurality of walls which constitute the manifold member 402 includes(in addition to the main side wall 408), a left side wall 424 (FIG. 5),a right side wall 426, and a dividing wall 428 which defines a boundarybetween the inlet manifold 412 and the outlet manifold 414 (and whichisolates the inlet port 404 from the outlet port 406). All of thesewalls are vertical walls. Also, the manifold member 420 includes a topwall 430 (FIG. 6) and a bottom wall 432, both of which are horizontalwalls.

Each of the inlet port 404 and the outlet port 406 may be integrallyformed in the main side wall 408, or may be formed by molding the mainside wall 408 around a suitable fitting, which is not separately shown.The inlet port 404 is positioned to allow coolant to flow into the inletmanifold 410, and may be configured to facilitate connection of acoolant line (not shown in FIG. 5) which transports coolant from a pump(not shown) to the microchannel assembly 100″. The outlet port 406 ispositioned to allow coolant to flow out of the outlet manifold 412, andmay be configured to facilitate connection to a coolant line (not shownin FIGS. 5 and 6) which transports coolant from the microchannelassembly 100″ to the heat exchanger (not shown).

The manifold member 402 may be coupled to the microchannel structure112″ and/or to a lid 434 (FIG. 6) via liquid-tight sealing arrangementsas indicated at 436 and 438. As in the previous embodiments, the sealingarrangement at 436 may be an O-ring, solder or an epoxy adhesive, forexample. The sealing arrangement at 438 may, for example, be formed ofsolder or an epoxy adhesive.

In some embodiments, the manifold member 402 may be formed as a singleunitary body, formed for example of a metal such as copper, or siliconor molded plastic.

The operation of a cooling system that includes the microchannelassembly 100″ may be generally the same as the operation described abovein regard to the microchannel assembly 100, except that the flow ofcoolant into, through and out of the microchannel assembly 100″ issomewhat different (and is also different from the flow through themicrochannel assembly 100′). Referring to FIG. 5, the coolant flowsthrough the inlet port 404 from an inflow coolant line (not shown) thatis coupled to the inlet port 404. The flow of coolant into the inletport is in the horizontal direction indicated by arrow 440. The coolantenters the inlet manifold 410 from the inlet port 404 and is distributedamong the microchannels of the first subset 416. The coolant flowsthrough the microchannels of the first subset in the same directionindicated by the arrow 440. While continuing to flow in the samedirection, the coolant exits from the microchannels of the first subsetat the rear end 420 of the microchannel structure 112″ and enters theintermediate manifold 423. The coolant flows through the intermediatemanifold 423 from the microchannels of the first subset 416 to themicrochannels of the second subset 418, and flows through themicrochannels of the second subset in a horizontal direction that isopposite to the direction indicated by arrow 440. The coolant flows outof the microchannels of the second subset and into the outlet manifold412. From the outlet manifold 412, the coolant flows out of the outletport 406, in the direction indicated by arrow 442, which is the samedirection in which the coolant flowed from the rear end of themicrochannel structure through the microchannels of the second subset.The coolant is transported away from the outlet port 406 via an outflowcoolant line (not shown) that is coupled to the outlet port 406.

FIG. 7 is a block diagram showing an IC die 710 and additionalcomponents of a cooling system 700. For purposes of illustration themicrochannel assembly 740 (which may be any one of the microchannelassemblies described above) is shown as a single block. The coolingsystem 700 includes a coolant circulation system 790 to supply thecoolant to the microchannel assembly 740. The coolant circulation system790 may be in fluid communication with the microchannel assembly 740 viaone or more coolant supply channels or lines 792 and one or more coolantreturn channels 794. Although not separately shown, a pump and a heatexchanger located remotely from the die 710 may be included in thecoolant circulation system 790.

Coolant supplied by the coolant circulation system 790 may flow throughthe microchannels of the microchannel assembly 740 at or above the rearsurface of the IC die 710 to aid in cooling the IC die 710. In someembodiments, the coolant is operated with two phases—liquid and vapor.That is, in some embodiments at least part of the coolant in themicrochannels is in a gaseous state. In other embodiments, the coolantis single phase—that is, all liquid.

The IC die 710 may be associated with a microprocessor in someembodiments. FIG. 8 is a block diagram of a system 800 in which such adie 810 may be incorporated. In particular, the die 810 includes manysub-blocks, such as an Arithmetic Logic Unit (ALU) 804 and an on-diecache 806. The microprocessor on die 810 may also communicate to otherlevels of cache, such as off-die cache 808. Higher memory hierarchylevels, such as system memory 811, may be accessed via a host bus 812and a chipset 814. In addition, other off-die functional units, such asa graphics accelerator 816 and a Network Interface Controller (NIC) 818,to name just a few, may communicate with the microprocessor on die 810via appropriate busses or ports.

The IC die 810 may be cooled in accordance with any of the embodimentsdescribed herein. For example, a pump 890 may circulate a coolant (e.g.,including water) through a cold plate 840 proximate to the IC die 810and having at least one microchannel to transport the coolant. The coldplate 840 may be constructed in accordance with any of the embodimentsof microchannel assemblies described above.

The system architecture shown in FIG. 8 is exemplary; other systemarchitectures may be employed.

The several embodiments described herein are solely for the purpose ofillustration. The various features described herein need not all be usedtogether, and any one or more of those features may be incorporated in asingle embodiment. Therefore, persons skilled in the art will recognizefrom this description that other embodiments may be practiced withvarious modifications and alterations.

1. An apparatus comprising: a microchannel structure havingmicrochannels formed therein, said microchannels to transport a coolantand to be proximate to an integrated circuit to transfer heat from theintegrated circuit to the coolant; and a plurality of walls coupled tothe microchannel structure to define a manifold that is in communicationwith at least a plurality of said microchannels, said plurality of wallsincluding a side wall, said side wall having a port therein, said portfor allowing coolant to flow in a direction, said direction being oneof: (a) into said manifold, and (b) out of said manifold.
 2. Theapparatus of claim 1, wherein said direction is parallel to a directionin which said coolant flows through said microchannels.
 3. The apparatusof claim 1, wherein said plurality of walls is included in a memberformed as a unitary body.
 4. The apparatus of claim 1, wherein saidplurality of walls is a first plurality of walls and defines a firstmanifold that is in communication with all of said microchannels, saiddirection being into said first manifold, the apparatus furthercomprising: a second plurality of walls coupled to the microchannelstructure at an opposite end of said microchannel structure from saidfirst plurality of walls, said second plurality of walls to define asecond manifold that is in communication with all of said microchannels,said plurality of walls including a side wall, said side wall of saidsecond plurality of side walls having a port therein, said port of saidside wall of said second plurality of walls for allowing coolant to flowout of said second manifold.
 5. The apparatus of claim 1, wherein: saidport is a first port; said manifold is open to all of said microchannelsat a first end of said microchannel structure; said side wall has asecond port formed therein to allow coolant to flow to a second end ofsaid microchannel structure that is opposite said first end; and saidcoolant flows out of said first port.
 6. The apparatus of claim 5,wherein said plurality of walls includes a horizontal wall to isolatesaid second port from said first port.
 7. The apparatus of claim 1,wherein: said port is a first port; said manifold is a first manifoldthat is in communication with a first subset of said microchannels thatincludes substantially half of said microchannels; said plurality ofwalls defines a second manifold adjacent said first manifold, saidsecond manifold being in communication with all of said microchannelsthat are not included in said first subset of microchannels; and saidside wall has a second port formed therein to allow coolant to flow intosaid second manifold.
 8. The apparatus of claim 7, wherein saidplurality of walls includes a vertical wall to define a boundary betweensaid first manifold and said second manifold.
 9. The apparatus of claim7, wherein said microchannel structure defines a third manifold that isin communication with all of said microchannels at an opposite end ofsaid microchannel structure from said first and second ports.
 10. Amethod comprising: flowing a coolant in a first direction out of aplurality of microchannels into a manifold; and flowing the coolant insaid direction out of said manifold.
 11. The method of claim 10, whereinsaid direction is horizontal.
 12. The method of claim 10, furthercomprising: flowing the coolant in said direction out of anothermanifold and into said plurality of microchannels.
 13. The method ofclaim 12, further comprising: flowing the coolant in said direction intosaid another manifold.
 14. A system comprising: a microprocessorintegrated circuit die; a network controller coupled to themicroprocessor; a microchannel structure thermally coupled to themicroprocessor integrated circuit die, the microchannel structure havingmicrochannels formed therein, said microchannels to transport a coolant;and a plurality of walls coupled to the microchannel structure to definea manifold that is in communication with at least a plurality of saidmicrochannels, said plurality of walls including a side wall, said sidewall having a port therein, said port for allowing coolant to flow in adirection, said direction being one of: (a) into said manifold, and (b)out of said manifold.
 15. The system of claim 14, wherein said directionis parallel to a direction in which said coolant flows through saidmicrochannels.
 16. The system of claim 14, wherein said plurality ofwalls is included in a member formed as a unitary body.
 17. The systemof claim 14, wherein said plurality of walls is a first plurality ofwalls and defines a first manifold that is in communication with all ofsaid microchannels, said direction being into said first manifold, thesystem further comprising: a second plurality of walls coupled to themicrochannel structure at an opposite end of said microchannel structurefrom said first plurality of walls, said second plurality of walls todefine a second manifold that is in communication with all of saidmicrochannels, said plurality of walls including a side wall, said sidewall of said second plurality of side walls having a port therein, saidport of said side wall of said second plurality of walls for allowingcoolant to flow out of said second manifold.
 18. The system of claim 14,wherein: said port is a first port; said manifold is open to all of saidmicrochannels at a first end of said microchannel structure; said sidewall has a second port formed therein to allow coolant to flow to asecond end of said microchannel structure that is opposite said firstend; and said coolant flows out of said first port.
 19. The system ofclaim 14, wherein: said port is a first port; said manifold is a firstmanifold that is in communication with a first subset of saidmicrochannels that includes substantially half of said microchannels;said plurality of walls defines a second manifold adjacent said firstmanifold, said second manifold being in communication with all of saidmicrochannels that are not included in said first subset ofmicrochannels; and said side wall has a second port formed therein toallow coolant to flow into said second manifold.
 20. The system of claim19, wherein said microchannel structure defines a third manifold that isin communication with all of said microchannels at an opposite end ofsaid microchannel structure from said first and second ports.